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This invention relates to wafer mapping systems.
Wafer mapping is an important element in semiconductor manufacturing. Each wafer may include many semiconductor chips and represent thousands of dollars worth of materials and time. Wafer mapping is a process wherein errors can be detected and addressed before significant manufacturing losses occur. As used herein, xe2x80x9cmapping wafersxe2x80x9d means scanning a set of wafers in either a transport or storage cassette or pod, and determining which slots in the cassette or pod have wafers in them and whether any of the wafers are incorrectly placed. Preferably, a device in accordance with embodiments of the present invention is mounted on a wafer-handling robot (a known robotic system used in wafer manufacture), and maps the wafers as the robot arm moves in a generally vertical path in front of the cassette or pod.
Wafer mapping systems use high-quality images to calculate location, thickness and correct slotting of one or more wafers. The amount of incident light that a wafer reflects can vary significantly. At one extreme, unprocessed wafers reflect a large portion of incident light. As processing steps add thin layers to the wafer""s surface, the wafer may only reflect a small fraction of the incident light. There are currently no fixed lighting schemes that can produce high-quality images for both kinds of wafers. As a result, known wafer processing systems cannot easily and accurately map both unprocessed and in-process wafers reliably.
A wafer mapping system includes an imaging array, at least one lighting module and a controller coupled to the imaging array and the lighting module. The controller is adapted to receive information relative to an initial acquired wafer image and adjust illumination from the lighting module based upon the initial acquired wafer image, and acquire a subsequent wafer image using the adjusted illumination.